Why? Marxism refers to the work of Marx and Engels, who are forefathers of the criticism of capitalism (along with other 18th century anarchists and socialists). I see no reason to get rid of the term or use other terms; I base my reasoning of Marx's work and Engels's formulations and I'll be sure to give the great men their credit.

I'm not making the case that Marxism had good ideas here, I'm making the case that Marxism had ideas that led to change in the direction it seems, without collapse, in the places where actual Marxism is a thing, and that the collapsed systems that called themselves Marxist shared a common deviation from Marxism on fundamental points stemming from their shared point of departure, Leninism.

Also, treating Marxism the way you suggest empowers the people who will use association with Marxism (which whether or not people who think Marxism had good ideas avoid the name, people who don't can still draw the connections) as an attack against an idea, leveraging the failure of Leninist societies to suggest that anything associated with Marxism is bad. So, no, I'll continue to point out that that involves not only the ad hominem fallacy, but also the fallacy of equivocation.

That kind of language policing is ridiculous. The words mean what they mean. If there is some taboo around a word like Marxism or feminism or islamism, that doesn't mean we need new words, it means there is resistance to the ideas. Over time the words depoliticize slightly and can be used freely again.

Giving in to people who are trying to cloud the meaning of words is the linguistic equivalent to negotiating with highjackers. You can do it, but you just make the job easier for the next highjacker.

I know it's a scary moment, where it feels like words have lost their meaning and insanity reigns, but that's just the zeitgeist. Words still mean things and that still had power.